1. Field of The Invention
This invention relates to a solids removal device and, in particular, to a solids collector and evacuator syStem for a settling tank.
2. Brief Statement of the Prior Art
Settling and clarification are unit operations which are practiced by municipalities and industrial concerns to remove suspended solids from liquids. In particular, water treatment facilities often incorporate settlers or clarifiers for treatment of fresh or waste water. When large volumes of water are treated, as typically encountered in municipal water and sewage treatments, the settling tanks are commonly inground tanks of cast concrete construction. In these settling tanks, various devices have been proposed to remove and collect the solids which are settled from the water during the treatment.
One common system employs a plurality of scrapers in the form of channels that are mounted on a continuous, driven chain which drags the scraper blades across the bottom surface of the tank, pushing the settled solids to removal station which has a hopper to collection the solids and a bucket elevator which scoops the solids from the hopper and lifts them from the tank.
Solids are usually detained in the aforedescribed solids removal system for times which exceed optimum detention times for biological applications. Additionally, the solids collection hopper is difficult to incorporate in some installations. Also the mechanical removal system has a high incidence of repair and maintenance requirements for its various mechanical components. Often the water being treated is corrosive and the latest systems have incorporated plastic (Nylon) gears and tracks and fiberglass scrapers. Another difficulty encountered with the aforementioned removal system is that when liquid which contains a large amount of solids is encountered, the solids can clog or obstruct the operation of the system, requiring operator intervention.